The MPEG (Motion Picture Experts Group) 1/2/4 and H.261/263 video coding standards require each macro-block to be coded as Intra after it has been coded as non-Intra for 132 times consecutively. This requirement reduces the propagation of visual artifacts generated by the IDCT (Inverse Discrete Cosine Transform) mismatch between the encoder and the decoder.
Low transmission delay is a very important requirement for two-way visual communication over a very low bandwidth channel. To limit the transmission delay and to reduce the bandwidth required for transmission, very few Intra frames are used. The lack of Intra frames generally results in very poor visual quality.
Sending an Intra frame every 132 times results in a bandwidth spike over the transmission line because the Intra frames are significantly larger than non-Intra frames. These bandwidth spikes can cause unwanted delays in the rendering of the signal. This is particularly unwanted for real-time applications, such as video conferencing, etc.
A frame is composed of many individual macro-blocks of data. Macro-block Intra refresh techniques are used to reduce the propagation of visual artifacts resulting from transmission over error prone channels. Macro-block Intra refresh is also used to address the problem of trans-coding compressed video bit streams, e.g., spatial-temporal resolution. However, these macro-block Intra refresh techniques propose very specific ways in which to select which macro-block is Intra refreshed.
Thus, there exists a need for improving visual quality of an encoded signal while reducing bandwidth spikes over low bandwidth channels. There exists a need for such a solution that also utilizes macro-block Intra refresh techniques in an improved manner.